Semi-conductor device



United States Patent "ice 3,483,439 SEMI-CONDUCTOR DEVICE John C. Kosco, St. Marys, Pa., assignor to Stackpole Carbon Company, St. Marys, Pa., a corporation of Pennsylvania No Drawing. Filed Oct. 18, 1967, Ser. No. 676,045 Int. Cl. H01] 3/00, 5/00, 3/12 U.S. Cl. 317-234 7 Claims ABSTRACT OF THE DISCLOSURE Semi-conductor devices provided by the invention comprise a crystal support of novel composition; a semi-conductor crystal, such as a silicon crystal, is fastened to the support. In accordance with the invention the supports comprise a sintered powder metal body consisting essentially of, by weight, about 43 to 58 percent of iron, about 24 to 33 percent of nickel, and a metal of the group copper and silver in an amount, by weight, from about 9 to 33 percent, the iron and nickel being present in the proportion by weight of about 1.78 parts of iron to one part of nickel, and the density of the body being at least about 93 percent of theoretical.

In solid state power rectifier devices, which may be considered as exemplifying semi-conductor devices in accordance with the invention, the support for the silicon crystal must possess mechanical strength and must also serve as a heat sink to conduct heat away from the semiconductor crystal. The support should also have a thermal coefiicient of expansion approximating that of the semiconductor, to minmize thermal failure. Materials which have been used to form semi-conductor supports are tungsten, molybdenum and some of their alloys. Some alloys, such as Kovar, have been preferred for this purpose; however, molybdenum and tungsten base materials are expensive and involve the use of critical raw materials. Additionally, they are relatively difficult to process because of the high temperatures involved in manufacturing. Furthermore, such materials present problems in finishing to size, Kovar-type alloys are also disadvantageous for this purpose because they possess relatively high electrical resistivity and the heating effects due to this characteristic limit their applicability as semi-conductor supports.

It is among the objects of this invention to provide supports for and semi-conductor devices including supports of improved electrical resistivity and better thermal conductivity than the support materials presently used, which do not require unduly expensive and strategically critical metals, which possess other properties requisite for such purpose, such as minimum porosity, and which may be made by powder metallurgy methods.

In accordance with this invention supports of improved utility for the production of semi-conductor devices are formed by compacting powder compositions of, by weight, about 43 to 5 8 percent of iron, 24 to 33 percent of nickel, and about 9 to 33 percent of copper or silver in which the iron and nickel are present in the proportions of, by weight, about 1.8 parts of iron to one part of nickel. The compacts are sintered in a reducing atmosphere, such as hydrogen, and the sintered compacts .are then repressed, or coined, to a density of at least about 93 percent of theory.

3,483,439 Patented Dec. 9, 1969 In the practice of the invention, iron and nickel powders, either as elemental iron and nickel or as a prealloyed powder of those two metals, in proportions approximating that of Invar (36 percent of nickel and 64 percent of iron, by weight) are blended with about 10 to 50 percent, by weight, of powdered copper or silver. The intimate mixture of powders is formed into compacts by pressing, say at about 10 to 40 tons per square inch (t.s.i.), and the compacts are sintered in a reducing atmosphere, suitably in the range from about 700 to 1100 C. in the case of the copper-containing compositions, or at about 800 to 1300 C. in the case of the silver-containing compositions. After being sintered the bodies are repressed or coined at, say 20 to 60 t.s.i., to minimize or eliminate continuous porosity in the bodies, which is achieved when the density of the coined body is at least about 93 percent of theoretical. Coining has the additional advantage of achieving parallelism and flatness of the support.

A major feature of supports made in this way is that they possess coefl'lcients of thermal expansion less than about 7.10- per degree C. at 300 C. My experience indicates that this value is sufiiciently close to that of pure silicon, 2 to 4.10- per degree C. to make these supports suitable for semi-conductor devices.

The use of copper or silver in accordance with this invention lowers the resistivity from approximately microhm-centimeters for pure Invar to 55, 25, 15 and 10 microhm-centimeters, respectively, for the compositions containing 10, 20, 30 and 40 percent silver. Similar reduction is also achieved with the compositions containing copper in the range stated. For example, supports of a 27 Cu-73 Invar alloy (about 47 percent of iron, 26 percent of nickel, and 27 percent of silver) was observed to have a thermal coefficient of expansion of 6.9.10 per degree C. at 300 C. and an electrical resistivity of 33 microhmcentimeters.

Semi-conductor devices are prepared by attaching silicon or other semi-conductor crystals to these supports in ways that are well known and used in the art.

According to the provisions of the patent statutes, I have explained the principle of my invention and have described what I now consider to represent its best embodiment. However, I desire to have it understood that Within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim: 1

1. A semi-conductor support comprising a sintered body of, by weight, about 43 to 58 percent of iron, about 24 to 33 percent of nickel, and about 9 to 33 percent of a metal of the group copper and silver.

2. A support according to claim 1, the support having a density of at least about 93 percent of theoretical.

3. A semi-conductor support according to claim 2, comprising, by weight, about 47 percent of iron, about 26 percent of nickel and about 27 percent of silver, and the support having a density of at least about 93 percent of theoretical, and a semi-conductor crystal attached to the support.

4. A semi-conductor device comprising a support consisting essentially of, by weight, about 43 to 58 percent of iron, about 24 to 33 percent of nickel and about 9 to 33 percent of a metal of the group copper and silver, and a semi-conductor crystal attached to the support.

4 References Cited UNITED STATES PATENTS 2,853,767 9/1958 Burkhammer 29-182 3,097,329 7/1963 Siemens 317234 JOHN W. HUCKERT, Primary Examiner R. F. POLISSACK, Assistant Examiner U.S. Cl. X.R. 

